Gear ring pump having a housing wall with a hollow cone recess

ABSTRACT

A gear pump has a gear wheel with teeth on an outer circumference and a second gear ring with teeth on the inside surface. The gear ring is guided in a circular-cylindrical recess of a housing and together with the gear wheel, each rotates about their own axis which are offset from one another. The gear pump is equipped with an intake opening and a crescent-shaped pressure opening in a first side wall of the housing that defines the recess. A countersunk feature is also provided, embodied as a hollow cone, in a second wall of the housing opposite the pressure opening. The hollow cone, which is in fluid communication with the pressure opening, promotes the buildup of a fluid film between the gear ring and the housing, which improves the wear resistance of the gear pump.

PRIOR ART

The invention is based on a gear pump which is driven by an electricdrive motor.

One such gear pump is already known (German Patent Disclosure DE 22 49395 A1), whose second wall of the housing is provided with countersunkfeatures of appropriate outline that are axially opposite both thecrescent-shaped intake opening and the crescent-shaped pressure openingof the first side wall. The countersunk features, embodied with sharpedges, have a bottom extending parallel to the end face toward the gearwheel of the side wall and the countersunk features have wallsprotruding upward at a right angle. The purpose of the countersunkfeatures is to compensate for axial forces engendered by the fluid to bepumped and exerted by the intake opening and in particular by thepressure opening on the gear ring, and to improve the running propertiesand the wear performance of the gear pump. However, the countersunkfeatures can be produced only at relatively great expense and aredesigned unfavorably from the standpoint of lubrication technology.

ADVANTAGES OF THE INVENTION

The gear pump of the invention has an advantage over the prior art thaton the one hand the countersunk feature can be created by metal-cuttingmachining using a simple tool, and on the other, a load-bearing film offluid from the countersunk feature can favorably form between the gearring and the second side wall of the housing, which considerablyimproves the wear resistance of the gear pump.

Expedient features and refinements of the gear pump of the invention areset forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

One exemplary embodiment of the invention is shown in simplified form inthe drawings and described in further detail below. FIG. 1 shows alongitudinal section through a pump unit with a gear pump, FIGS. 2 and 3show sections through the gear pump taken along the line II—II in FIG. 1and III—III in FIG. 2, respectively, on a larger scale than in FIG. 1.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

A pump unit 10 has a gear pump 11 in a two-part housing 12 and also hasan electric drive motor 13 (FIG. 1) which is secured to the two-parthousing. The gear pump 11 is formed by a gear wheel 14 with teeth on theoutside circumference and by a gear ring 15 with teeth on the inside.The gear pump 11 is of the crescentless internal gear pump (Gerotorpump) type. Its gear ring has a finite number of teeth 16 and a number,less than that by one tooth, of teeth 17 of the gear wheel 14. The gearwheel 14 and the gear ring 15 are received in a circular-cylindricalrecess 18 of a first part 19, remote from the motor, of the housing 12.Toward the drive motor 13, the recess 18 is closed off by a second part20 of the housing 12. The gear wheel 14 is disposed in a manner fixedagainst relative rotation on a pump shaft 21, which is coupled to thedrive motor 13 and is guided in the housing 12.

The gear wheel 14 and the gear ring 15, which mesh with one another, canbe driven clockwise, in terms of FIG. 2; the gear ring is set intorotation by the driven gear wheel. The gear wheel 14 and the gear ring15 have axes 24 and 25, respectively, that are offset from one another.The axis 24 of the gear wheel 14 is at the same time the axis of thepump shaft 21, while the axis 25 of the gear ring 15 coincides with theaxis of the recess 18. The recess 18 is axially defined by a first sidewall 26 of the housing part 19 (FIG. 3). At the same time, the housingpart 19 forms a jacket wall 27 that radially guides the gear ring 15.Finally, on a side opposite the first side wall 26, the recess 18 isdefined by a second wall 28, formed by the housing part 20. The firstside wall 26 and the second side wall 28 take on the axial guidance ofthe gear wheel 14 and the gear ring 15.

In the first side wall 26 of the housing part 19, an intake opening 31and a pressure opening 32 for hydraulic fluid to be pumped by the gearpump 11 are formed. The openings 31 and 32, which in the view of FIG. 2are located in front of the plane of the drawing and are thereforesuggested by dot-dashed lines, each have a crescent-shaped outline andextend approximately concentrically to the axes 24 and 25 of the gearwheel 14 and gear ring 15. The intake opening 31 and the pressureopening 32 each extend over about 150° of the circumference of the gearwheel 14 and gear ring 15. In the circumferential direction, the twoopenings 31 and 32 assume a mutual spacing which is equal to at leastone tooth spacing. The intake opening 31 and the pressure opening 32change their radial width over their course. The pressure opening 32, inthe direction of rotation (clockwise) of the gear wheel 14 and the gearring 15, successively has an inlet zone 33, a middle zone 34, and anoutlet zone 35. The inlet zone 33 has a greater radial width than themiddle zone 34, and the outlet zone 35 is narrower than the middle zone34.

A countersunk feature in the form of a hollow cone 38 is locatedopposite and in fluid communication with the pressure opening 32 in thesecond side wall 28 of the housing part 20. The hollow cone 38 has anopening that is toward the recess 18; the axis 39 of the hollow cone 38extends parallel to the longitudinal axis 25 of the recess 18. Thehollow cone 38 has a cone angle of about 120°. The orifice cross section(diameter) of the hollow cone 38, which with a jacket wall is adjacentto the recess 18, and is selected such that the hallow cone is overtakenat least by the full radial width of the gear ring 15. In the exemplaryembodiment shown, the orifice cross section of the hollow cone 38,beginning at the jacket wall 27, extends toward the axis 25 to beyondthe toothed ring of the gear wheel 14 (FIG. 2). It can also be seen fromFIG. 2 that the orifice cross section of the hollow cone 38 extends asfar as the radially inner boundary wall 40 of the pressure opening 32.

The hollow cone 38 is disposed in the side wall 28 of the housing part20, opposite the middle zone 34 of the pressure opening 32. In operationof the gear pump 11, the fluid pumped by the gear wheel 14 and gear ring15 reaches both the pressure opening 32 and the inside of the hollowcone 38. Because of the rotary motion of the gear wheel 14 and inparticular the gear ring 15, the fluid is carried out of the hollow cone38 and forms a film that supports both the gear wheel and in particularthe gear ring on the side wall 28. At the same time, fluid also entersthe gap between the jacket of the gear ring 15 and the jacket wall 27 ofthe housing part 19. The fluid film forms a load-bearing layer, so thatthe area of mixed friction upon startup of the gear pump 11 is rapidlytraversed and is avoided during pump operation. At the same time, thefluid film creates a load- bearing layer, which at least partlycompensates for axial forces acting on the gear ring 15 from thepressure opening 32.

As already suggested, the diameter of the hollow cone 38, its coneangle, and its location in the recess 18 can all be selected in a mannerdeparting from the exemplary embodiment. For instance, the cone anglecan be varied within the limits of 90 and 150°, to exert influence onthe drag flow that carries fluid out of the hollow cone. Furthermore,the hollow cone 38 can be shifted into the region of the inlet zone 33of the pressure opening 32. With respect to the course of the fluidpumped by the gear pump 11, this achieves an earlier building in thefeeding direction of the supporting fluid film under the gear ring 15.The foregoing relates to a preferred exemplary of embodiments of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

What is claimed is:
 1. A gear pump (11) including first and secondhousing parts (19, 20), a gear wheel (14) with teeth on an outsidecircumference and a gear ring (15) with teeth on an inside surface, thegear ring is guided in a circular-cylindrical recess (18) of a housingpart (19) and together with the gear wheel (14) rotates about their ownaxis (24, 25) which are offset from one another, an intake opening (31)and a crescent-shaped pressure opening (32) in a first side wall (26),defining the recess (18), of the first housing part (19), and acountersunk feature (38), opposite and in fluid communication with thepressure opening (32), in a second wall (28) of the second housing part(20) that defines the recess (18) on another side, and the countersunkfeature is embodied as a hollow cone (38).
 2. The gear pump of claim 1,in which the hollow cone (38) has a cone angle between 90 and 150°. 3.The gear pump of claim 2, in which the hollow cone (38) is disposed withan axis (39) extending parallel to an axis (25) of the recess (18). 4.The gear pump of claim 1, in which the orifice cross section of thehollow cone (38) is overtaken at least by the gear ring (15).
 5. Thegear pump of claim 1, in which the orifice cross section of the hollowcone (38) is overtaken by the gear ring (15) and at least by the teeth(17) on the gear wheel (14).
 6. The gear pump of claim 1, in which thehollow cone (38) is disposed in the middle zone (34) of the pressureopening (32).
 7. The gear pump of claim 1, in which the hollow cone (38)is disposed in the region of the inlet zone (33) of the pressure opening(32).